A traditional maximum power point tracking (MPPT) algorithm sees a solar array as if it were a single solar module. MPPT can pull and push current on all strings and solar modules in a solar array in an equivalent fashion. As such, if solar modules in the solar array operate at different working points on the I-V curve, due to differences in installation, fabrication, or degradation over time, an MPPT algorithm may not be able to find the maximum power point (MPP) for the solar array.
U.S. Pat. No. 7,602,080, issued on Oct. 13, 2009 and entitled “Systems and Methods to Balance Solar Panels in a Multi-Panel System,” discloses a local management unit for a solar module. The local management unit has a controller for controlling the operation of the solar module and a link module unit to provide connectivity to a power bus for energy delivery and/or for data communications. The entire disclosure of U.S. Pat. No. 7,602,080 is incorporated herein by reference.
In some situations, in solar panels, a simple, economical solution is desirable to reduce both power consumption and component cost for the circuitry supplying a controller, etc., running in the solar panels. Further, it is desirable that such a solution offer high reliability and high efficiency.
Further, it is desirable, for safety and security, that modules may be added only to panels that are compatible with those modules, to avoid electrical problems and reduce potential fire danger, as well as to help protect in some cases against theft or misuse.
In addition, during emergency shutdown one of the problems that can occur is that even through the panels are shut down, there may be substantial voltage and energy stored in the input capacitors of the inverter. Thus even though the panels have been turned off, there may be enough energy and voltage remaining to kill a person that might come in contact with the wiring. For example, a firefighter who tries to create an opening in the roof may cut through one of the wires. To avoid this problem, emergency shut off switches have been provided, but typically, such switches only shut off the panels; they don't necessarily clear out the remaining energy in the capacitors. Because the input voltage can go up to 500 to 1000 volts, and the capacitors are quite substantial to support smooth operations, the stored energy may kill several people. Thus, it is also desirable to quickly remove the stored energy from the input capacitors of the inverter.
U.S. Pat. App. Pub. No. 2016/0156308 discloses a junction box for a solar panel, where the junction box can use any of a plurality of a replaceable or interchangeable junction box covers that host replaceable or interchangeable control circuit modules for the solar panel. It is desirable to have reliable and yet inexpensive contacts for establishing connections between the power lines hosted in the junction box and the control circuits provided in the junction box covers.